The present invention relates to a magnetic recording medium implemented as a disk, drum, tape, etc.
There is an increasing demand for a magnetic disk drive or similar magnetic recording device having a smaller size and a greater capacity. To attain both the smaller size and the greater capacity, high recording density is the prerequisite. For this purpose, even a magnetic disk drive using a perpendicular magnetic recording system in place of the traditional longitudinal magnetic recording system has been reported. The key to high recording density is to reduce the gap between a magnetic head and a magnetic medium. Specifically, the vertical recording system cannot fully exhibit its inherent advantage unless a gap smaller than 0.1 .mu.m is implemented. Of course, reducing the gap is also essential with the longitudinal magnetic recording system in enhancing high density recording. More specifically, reducing the the floating amount of a magnetic head slider and the thicknesses of magnetic medium and protection layer of a magnetic disk are the major technical issues in the magnetic recording art.
Basically, a magnetic disk using a thin film magnetic medium arid put to practice today has a 1 nm to 2 nm thick lubrication layer, a 30 nm to 50 nm thick protection layer, a 50 nm to 70 nm thick metallic magnetic medium, a 20 .mu.m to 30 .mu.m thick nonmagnetic NiP layer, and an Al alloy substrate. Typically, the lubrication layer is implemented by a liquid lubricant belonging to a group of organic fluorides, the protection layer is implemented by a carbon film or an SiO.sub.2 film formed by sputtering, and the magnetic medium is implemented by a Co-based alloy thin film formed by sputtering or nonelectrolytic plating.
Conventional magnetic disks with the above-stated laminate structure have some problems left unsolved, as enumerated below.
(1) When a magnetic disk drive is brought to a stop, an attraction acts between the liquid lubricant and the head slider, tending to cause the slider to stick to the surface of the disk. In the light of this, it is a common practice to provide crevasse-like scratches called a texture on the surface of the disk. However, the texture not only increases the gap between the disk and the slider but also degrades reliability in the mechanical durability aspect.
(2) The liquid lubricant is apt to fly away due to the spinning disk (phenomenon called spin-off). Although the lubrication layer is provided with a thickness taking account of the spin-off of the lubricant, a thick lubrication layer aggravates the above drawback (1).
(3) The range of substances applicable to the protection film is extremely narrow since the spin-off characteristic and lubricating ability of the liquid lubricant depends on the bond between the lubricant and the surface of the protection layer. Particularly, a fluoric liquid lubricant which is predominant today provides molecules with bonding ability by a functional group and, therefore, does not surely bond to the carbon-based or oxide-based nonmagnetic protection layer.
Since the problems stated above stem from the fact that the lubricant is a liquid, the use of a solid lubricant is under study. However, a solid lubricant brings about other problems, as follows, When the disk starts and ends spinning, it causes a solid lubricant to come off by contacting the lubricant. Then, the particles of the lubricant would contaminate the inside of the device while degrading reliability. Moreover, a solid lubricant does not have a self-recovering ability available with a liquid lubricant. The self-recovering ability is such that a liquid lubricant becomes thin on the slider trace, but as the slider moves to another locus, the lubricant automatically gathers at the thin portion from around it. For these two reasons, the application of a solid lubricant to a magnetic disk has not progressed at all.